The invention relates to apparatus for applying sprays of coating material to workpieces. More particularly, the invention relates to improvements in apparatus of the type wherein a mask is used to intercept that part of the spray which bypasses the workpieces.
It is known to apply sprays of coating material, such as photosensitive resists and solder resists, to copper-lined conductor plates or like workpieces by means of a rotary atomizer and an electrostatic field. The mask which is used in such apparatus is a belt or band conveyor which consists of a web of paper and transports the workpiece along a horizontal path beneath and past the coating station. Thus, the paper web performs the dual function of transporting the workpieces and of intercepting that part of the spray which bypasses the moving workpieces. Interception is necessary in order to avoid contamination of the area beneath the coating station. As a rule, the apparatus comprises a grounded electrode which is installed at a level below the path of the workpieces and the paper web.
A drawback of such apparatus is that they consume large quantities of masking material. This is due to the fact that the paper web serves as a conveyor for the workpieces and, therefore, its speed must match the speed of transport of workpieces past the coating station. The rate of consumption of web material is directly proportional to the speed at which the workpieces are transported toward, past and beyond the coating station.